The purpose of this double-blind, dose-controlled, multicenter study is to evaluate the dose-response and efficacy characteristics of gabapentin in patients with complex partial or secondarily generalized seizures by conversion from marketed anti-epileptic drug therapy to either minimum-effective dose, medium dose, or high dose (2400 mg/day) gabapentin monotherapy; and to assess the safety of gabapentin in patients undergoing reduction in marketed anti-epileptic drug therapy and in patients receiving gabapentin monotherapy.